Indolent lymphoma is a slow growing but incurable lymphoma which includes follicular lymphoma and marginal zone lymphoma. Follicular Lymphoma and Marginal zone lymphoma are cancers of the B lymphocyte, a type of white blood cell. Lenalidomide is an immunomodulatory drug (a drug that affects the immune system) which alters the body's immune system and it may also interfere with the development of tiny blood vessels involved in tumor growth. Therefore, lenalidomide may reduce or prevent the growth of cancer cells. Lenalidomide has also been shown to restore the immune cells' ability to attack and kill tumor cells, an ability that may be inhibited by follicular lymphoma and other lymphomas. The combination of rituximab and lenalidomide may eliminate the cancer while restoring the immune system's ability to attack tumor cells.